A known agitating mechanism, such as the agitating mechanism of a food mixer, rotates in a fixed single direction, or can be direction-reversed. However, the direction reverse is achieved either by manual trigger or according to a fixed time period.
In real life, when some agitating mechanisms are used to agitate blocky solid food such as vegetables and meat blocks, or food containing the solid blocks, agitating blades of the agitating mechanism may be resisted by the blocks. The agitating mechanism usually operates with a preset or user-selected power which is constant. When the agitating blades are resisted by the solid blocks, the rotation speed becomes very slow or even the agitating mechanism becomes stalled which is referred to as being jammed. If the jam lasts a little long, it may cause the agitating mechanism (e.g. the motor) or other electrical components to be burnt out. Even if the agitating blades of the agitating mechanism forcefully breaks through the resistance of the solid blocks, this over-forceful driving manner can seriously damage the texture of the food being agitated, which reduces visual enjoyability of the food, affects user's appetite, degrades the user experience, and shortens the life of the agitating mechanism.
Some other agitating mechanisms are used to agitate mushy and viscous food such as milkshake or salad, and usually ice blocks are added to the food to be agitated at the same time. During agitation, high rotation speed agitating blades (cutter blades) form a blocking layer, which makes the viscous food unable to be sufficiently agitated and always remain above the blocking layer of the cutter blades. As such, a cavity is formed in the agitated substance at the area of the blocking layer, which looks like an air bubble in the agitated substance. The cavity does not hinder the agitation of the agitating mechanism. However, the cavity makes the substance unable to be homogenously agitated, such that fine agitation cannot be achieved, which can easily result in lumps being formed in the agitated substance.